Electrooptical system



July A26, 14932. F. GRAY ELEcTRooPTIcAL SYSTEM Filed Jan. 25. 1930 /N VE N TUR A from/Ev? Patented July 26, 1932 UNiTED? STATES FRANK GRAY, F NEW YORK, N. Y., ASSIGNOR TO BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y.,.AV CORPORATION 'OF NEW YORKv ELECTROOPTICAL SYSTEM Application led January 25, 1930.v Serial No. 423,295.

i This invention relates to electro-optical systems and particularly to transmitting apparatus therefor. f

The invention contemplates the production y ofaphotoelectric current of carrier frequency modulated in accordance With the light intensities of an object to be transmitted.

It has heretofore been proposed to accomplish the result described above either by l1 0 chopping thelight beam at a carrier frequency rate, before or after the scanning process, or by electrically energizing the photoelectric cell with a current of carrier requency.

kAnother-proposal includes the use of .an oscillatory current for yenergizing a source supplying a. field or obj ect with light, Which is thereby varied in accordance With the tone values of the elemental areas of an object or held. The doubly variedvlight is applied to a photoelectric cell to produce current Which is used to modulate a carrier Wave. l lIn accordance With va preferred embodiment of the present invention, the light source is energized by a current of carrier frequency to provide illumination for a field or object to be scanned at a transmitting station. |The light radiations', varying at carrier frequency and also in accordance With the tone values of elemental areas of the eld or object, are then applied to a photoelectric cell, which is thereby controlled to Aproduce a carrier frequency current modulated in amplitude in accordance with the tone values of the eld.

An object of the invention is to control the production of photoelectric currents by radiations from a prime source of light which Varies at a carrier frequency rate and also as the tone values of an object or eld to be transmitted.

A feature of the invention relates to the provision of a light source, energized by current of carrier frequency for illuminating an object to be transmitted, as a means to control the production of photoelectric currents.

. more detailed description of the invention follows and is illustrated in the attached drawing, in which Fig. 1 illustrates a television transmitter iny which the object is scanned by a spot of light,

F ig is flood lighted; A

Fig. 3 illustrates a system for supplying current to the illuminating source, and

F ig. 4 shows an-amplifier Which may be used with the system of Fig.

ln Figure 1, the subject 1 to be trans-,

mitted is illuminated by a lighting device 2,

supplied With current by vfa high frequenc current source 3. -f

. 2 is' Similar toy-Fig, 1, but the tjah The subject'may be a human being, either still or moving or a scene Aincluding still or animated objects. The device'2 may be any lamp adapted to produce light radiations fluctuating at high frequency vvhen supplied withcurrent from .the source 3. An induction lamp of the type disclosedin U. S. Patent 966,204 Aug'. 2, 1910 to Hewitt is `suitable for this purpose. High frequency current may be supplied from any Wellv known source, a vacuum tube oscillating system constitutes such a source.4

The light source 2 is imaged by a lens 4 upon the scanning disc 5, provided with a series Vof apertures arrangedgin a'spiral line. The light radiations, passing through the perforations of the disc 5, are concentrated by a lens 6 into an intense spot of light.

As disclosed in U. S. application Serial No. 227 ,649 filed October 21, 1927 by F. Gray, the disc 5 operates to cause the spot of light to transverse successive parallel lines of the Vsubject 1. The disc is driven ata rate of speed such that thejvsubjectvis completely scanned a number of times per second, corresponding to the persistence of vision.

The light reiiected from the subject lis applied to `and serves to activate the Vphotoelectric cells 7. CurrentV is supplied to the space path' Within the photoelectric cells 7' by the source 11, herein shown "by Way of eX- ample as a battery. Since the light produced esi by the lamp 2 fluctuates in intensity in step With the current supplied by the source 3 and is further ycaused to vary las the tone values of elemental 'areas of the subject'1, the photoelectric cells 7 Will' be activated to produce Ya high frequency current having its amplitude modulated in accordance with the varying tones of the subject. l

The modulated highfrequency current is supplied to the input electrodes of an amplifier 8, herein shown as a two-stage amplifier including space discharge'tubesl The filaments of the tubes, included in amplifier 8, are. heated by any suitableA source, (not shown), grid-biasing potential is supplied by the tubes by the sources 12 and space current is supplied thereto by the source 13.

Obviously the amplifier 8 may include amplifying devices of any type. n requirement is that they repeatthe modulatedwave without distortion. Again, one or any Vnumber of stages may be used. The input circuit of each stage of the amplifier includes a loop circuit tuned to the frequency minated by fiood lights.

' cells.

ofthe impressed wave whereby the photo- Aelectrically producedv amplitude modulated highjfrequency wave isselectively amplilied. After being amplified to the required degree, the modulated wave is supplied to a transmission circuit 10, which may be associated with an lantenna or a line.

' The system of Fig. 2 Vdiflersfroin that of Fig. 1, mainly in that the subject 1 is illuln other words, the subject is completely illuminated at all times. For this purpose two induction lamps 14 areused. These lamps are suppliedwith current by the high frequency source 15.

The lens 16 serves to'image the subject 1 upon `the scanning disc 17, provided with a spiralrow of apertures. The uisc 17 is driven atar rate of seed .such that the subject is completely scanned a number oftimes per second, corresponding to the persistence of vision. The light passing through the spiral of apertures is cencentrated by the lens 18 upon the photoelectric cell system 19, which may include any desired Vnumber of rlhe photoelectric cell system 19 is controlled to produce a carrier wave, modulated in amplitude by image currents corresponding to tone values ofthe elemental areas of the rsubject 1. As in the system of Fig. 1, the carrier modulated wave is amplified in Y theamplifier indication by 2O and supplied Vee to a transmission circuit.

In general induction lamps require the use of an energizing current of such high-r frequency. that it cannot be efficiently transmitted to a remote receiving station over a. line. Fig. 3 illustrates an apparatus 21 for producing current, which may be used to energiZe induction lamps so that they produce light radiations varying at a frequency which may be efficiently transmitted over a line.

Hence by substituting this Vsource for that shown at 3 or 15,7the systems of Fig. lor Y2may be made available for use with atransmission line.

The only The apparatus of Fig. 3 comprises a space` discharge oscillator 22 and a modulator tube 23, the output circuits of whichl are supplied `ing a filament, al grid, and anl anode associated with a tuned circuit 27 which serves in general todetermine the frequency of the oscillations generated. These may be of high frequency suitable for-energizing an induction lamp. The input circuit of the modulator 23 is supplied with a current of`line carrier frequency by a 'source 28. l s

The above described system operates inthe manner disclosed in U. S. Patent 1,442,147, issued January 16, 1923 to Heising, to combine the line carrier current supplied y by the source 28 with" the high frequency oscillations generated by the oscillator 22.v This system will operateto produce, in they plate circuit of the oscillator, a'current of line carrier frequency, acurrent of high'frequency and two sidebands having frequencies respectively equall to the sum and the vdifference of the carrier and high frequencies. V By substituting the source 21 for the source 3 or 15 of Figs. 1 andA 2 respectively, the induction lamps will be energizedto produce Y resistance coupled space discharge tubes, the

constants of the circuit being so chosen that it operates more efficiently Vas an amplifier of the components of line carrier frequency than the components ofhigh'frequency. Y

As illustrated, the ampliiier consists' of two space dischargetubes 31'and 32 intercoupled by resistances 33 and 34, respectively, in shunt to the output electrodes of one tube and the input electrodes of thev succeeding tube. rl`he lead connecting the upper terminals ofthe resistances 33and 34 includes a series condenser 35. The photoelectric jcell system may be included in or coupledto the Y input circuit ofj the tube 31. A battery 36 supplies space current tothe photoelectric cells. The filaments of tubes 31. and 32are supplied with heating current from 'any suitable source, not shown. Biasing otentials areas of a subject, the light supplied by said are supplied to the grids of the tu es by the lamp-to said light sensitive devlce.

batteries 37 and current is supplied to the space paths Within the tubes by the source 38, herein shown as a battery.

Obviously the amplifier circuits could be A tuned to the line carrier frequency, i. e. either the input or output circuit or both could be provided with a tuned circuit. In this case the amplifier would selectively amplify the line carrier Wave While the high frequency Wave would be sharply attenuated.

As a matter of fact the system of Fig. 3 provides a means for simultaneously producing a high frequency carrier Wave and a line frequency carrier Wave each modulated by the tone values of the subject to be transmitted. It therefore provides a means whereby currents modulated by the same image variations may be simultaneously supplied for transmission over a radio link and over a transmission line.

What is claimed is:

l. A transmitter for an electro-optical system comprising an induction lamp, means for energizing said lamp With composite current including components of high and line carrier frequencies, a light sensitive device, and l means for controlling by elemental areas of a subject to be transmitted the light supplied from said source to said sensitive device.

2. A transmitter for an electro-optical system comprising an induction lamp, a source for supplying said lamp with energizing current of high frequency modulated with a current of line carrier frequency, a light sensitive device, and means for controlling, by elemental areas of a subject to be transmitted, the light supplied by said lamp to said sensitive device to cause the production of a line carrier Wave modulated in accordance with said elemental areas.

3. An electro-optical apparatus comprising an induction lamp, a source supplying said lamp With energizing current simultaneously varying at different frequencies, a light sensitive device, and means for controlling, by elemental areas of a subject, the light supplied by said lamp to said light sensitive device.

4. An electro-optical apparatus comprising an induction lamp, a source supplying current simultaneously varying at high and line carrier frequencies, a light sensitive device, and means for controlling, by elemental areas of a subject, the light supplied by said lamp to said light sensitive device.

5. A11 electro-optical system comprising an induction lamp, a source supplying said lamp With energizing current having components of different frequencies each of which is of constant amplitude, a light sensitive device, and means for controlling, by elemental In Witness whereof, I hereunto subscribeA my name this 22 day of January, 1930.

FRANK GRAY. i ,o 

